1. Field of the Invention
The invention relates to a data processing system including an input device with a touch screen for inputting data into the system by means of touch, and a digitizing tablet for inputting data into the system by means of manipulation of a stylus near a tablet area, wherein the touch screen area and the tablet area are at least partly overlapping.
2. Description of the Related Art
Systems employing a touch screen as a data input device are widely known. By touching the touch screen at a predetermined position with a finger, or with an object having a similar operation with respect to the touch screen, data are selected that are indicative of that particular position. Thereupon the associated data are introduced into the system and are processed. A touch screen may be combined with a display for selecting data according to the zones shown on the display, such as virtual buttons. Also, the display may function as a means for providing visual feedback to the user by showing the information pertaining to the data after processing. On the basis of the mechanism for activating the touch screen several types of touch screens can be distinguished. Touch screens of a first type are those that require for activation an actual contact between the finger of the user or another object and the screen. An example of such a touch screen employs the localization of the absorption of surface acoustic waves propagating in a front-panel, the absorption occurring as consequence of the contact between the panel and a soft tissue such as the user's finger. Another example of a touch screen of the first type is a screen wherein the reaction-forces and reaction-moments, occurring in the suspension of the screen when it is touched, are registered for deriving the location of the contact.
For touch screens of a second type the presence of an object, such as the user's finger, in the proximity of the screen is sufficient for enabling the activation of the touch screen without an actual contact. An example of such a touch screen uses a grid of light beams (infrared) in front of and parallel to a front-panel. The presence of an object at a particular location in the grid is detected upon the blocking of lightbeams associated with that particular position. In another example of a touch screen of the second type the user's finger in the proximity of the touch screen establishes a capacitive coupling towards ground, which coupling can be detected and localized.
Therefore, the term "touch" in this text will incorporate: "manipulating an object in the detection range of", in addition to: "establishing an actual contact with".
It is a disadvantage of the conventional systems that these are not suitable for both a data-input by means of touching the touch screen at predetermined zones, like virtual buttons, with a finger or a similar object suitable for pointing, and a data-input by means of writing, drawing or accurate pointing on the screen with a suitable stylus. In other words, the touch screens of the known systems cannot represent a virtual control panel with buttons, or a keyboard as well as a digitizing tablet.
Writing or drawing in an ergonomically justified way implies that the writer's or drawer's hand is supported by a surface more or less coinciding with the area to be written upon. The known touch screens requiring an actual contact for activation will register simultaneously the contact of the stylus with the screen and the contact of the writer's hand with the screen without discriminating between the two impressions. The known touch screens that are activatable by manipulating an object, like the user's finger, in front of the screen cannot discriminate between the stylus and the user's hand either. For example, both the hand and the stylus intercept the light beams of the grid that couples a plurality of light transmitters with a plurality of associated light detectors, or both enable a capacitive coupling towards ground.
Also the touch screen and the digitizing tablet operate with mutually different resolutions on stimuli, since the accuracy of a touch depends on the dimensions of a finger (order of magnitude: 1 cm) and the accuracy of a data entry with a stylus depends on the dimensions of the cooperative part of the stylus (order: 1 mm or even smaller).